#simulate population sizes, true means, and observed means
library(tidyverse)
library(truncnorm)

#sim data
d = tibble(
  n = runif(1e4, min = 2, max = 100) %>% round(),
  true_mean = rnorm(1e4, mean = 100, sd = 15),
  observed_mean = NA
)

#sample the means
d$observed_mean = map2_dbl(d$n, d$true_mean, ~mean(rnorm(.x, mean = .y, sd = 15)))

#plot
ggplot(d, aes(true_mean, observed_mean, color = n)) +
  geom_point(alpha = .5)